The present invention is in the field of microscopy, specifically in the field of electron beam microscopy (EM) and Scanning Transmission X-ray Microscope (STXM), and in particular Transmission Electron Microscopy (TEM). However its application is extendable in principle to any field of microscopy, especially wherein characteristics of a (solid) specimen (or sample) are studied in detail, such as during a reaction.
Microscopy is a technique used particularly in semiconductor and materials science fields as well as for biological samples for site-specific analysis, and optionally deposition, and ablation of materials. Also it is widely used in life sciences to obtain information. The resolution domain is typically from 0.1 nm to 1 μm. In microscopy typically a source is used to obtain an image. The source may be a source of light, electrons, and ions. Further scanning techniques have been developed using e.g. atomic force (AFM) and scanning tunnelling. Under optimal conditions a modern microscope can image a sample with a resolution typically in the order of a few tenths of nanometres for a TEM, a nanometre for a FIB and Scanning (S)EM, and a few hundred nanometres for an optical microscope.
The present invention relates to micro-reactors and nano-reactors, i.e. having a reaction volume in the order of 10−9 m3. Reference throughout the description to a reactor refers to said micro-reactors and nano-reactors. Typically a to be observed sample is positioned in a reactor; the sample is typically attached to a second wall, the bottom, and above the sample between the bottom and first wall, the top, a (virtual) column is present through which an observation is made.
A problem with prior art microreactors, especially when used in an environment having a substantially different pressure from the inside of the reactor, is that the thin observation windows and/or reactor wall (or membrane) tend to bulge outwards or inwards, depending on the environmental pressure. Bulging can be in the order of several μm-100 μm, thereby extending/shrinking a (virtual) column above/beneath a sample. Especially the outward bulging can be much larger than a height of the original column. Such is especially the case for gas and liquid nanoreactors for in-situ transmission electron microscopy experiments. Such nanoreactors typically consist of two thin membranes, which allows one to enclose a gas or liquid in between the membranes and still maintain a very good vacuum in the electron microscope. One of the big problems in the use of gas and liquid nanoreactors in an electron microscope is that the electron transparent membranes are bulging outwards due to the pressure difference between the microscope (ultra-high vacuum) and the inside of the nanoreactor (for instance 1 bar). Whereas one prefers gas columns of less than 5 μm and liquid columns of less than 0.5 μm, the bulging can lead in to column lengths of 20 μm and more.
WO2011019276 (A1) recites a method of manufacturing a micro unit for use in a microscope. The method comprises the step of providing a planar substrate supporting structure and creating a chamber in the supporting structure for receiving a fluid containing a chemically reacting substance to be inspected. Further, the method comprises the step of coating an inner surface of the chamber with a thin layer. The method also comprises the step of locally removing material from the exterior of the supporting structure until the thin layer is reached for forming a window segment that is at least partially transparent to a beam of radiation generated by the microscope. It has been found that such a micro unit allows one to prevent bulging of the membranes away from each other. However, the micro unit is found to be impractical; the sample has to be loaded by use of a liquid suspension of particles of interest and therefore there is no control on a final position of the sample and as a result the sample is typically positioned where it can not be observed; and the sample is not positioned at a desired location where it can be manipulated properly, such as by heating, by performing a reaction, etc.; and the manipulation of the sample cannot be controlled properly, such because heating is non-uniform. With some materials this approach may be useful, but for many others it is required to put a sample into the nanoreactor at a very special location. Thus this method is not very useful for most applications.
EP 2 626 884 A1 recites a method for fabricating a microfluidic chip for transmission electron microscopy, which has a monolithic body with a front side and a back side. The monolithic body comprises an opening on the back side extending in a vertical direction from the back side to a membrane on the front side, the membrane being supported at edges of the opening and extending across the opening, and a microfluidic channel comprising on top of the membrane a sample chamber with a top window towards the front side and a bottom window towards the back side, the top and bottom windows being aligned with each other so as to allow for observation of a sample volume between the top and bottom windows inside the sample chamber in a transmission configuration along an axial direction, wherein the dimension of the membrane in at least one horizontal direction exceeds the dimension of the sample chamber in that direction. Clearly the sample itself must relate to a liquid or gas, which can only be introduced into the chamber by microfluidic action of the chip. Certain drawbacks are still present in this device, such as not having control on the parallel positions of the membranes. This document inherently relates to a monolithic body with a reactor having internal pillars for controlling bulging and considers c.q. teaches no other options for controlling said bulging. Also this document shows the feasibility of using a piezoelectric layer for a totally different purpose, i.e. a strain gauge for determining the deformation of the window, without mentioning a further use thereof. It is known however that semiconductor strain gauges are fragile, i.e. break easily, and therefore have limited use. If a strain gauge foil would be intended, than this type of foil is not considered suited for nanoreactors.
Oh et al. in Journal of micromechanics and microengineering in March 2006, p 13-30 gives a brief overview of micro valves, including a piezoelectric actuated microvalve. Therein microvalves were employed for gas flow regulations, i.e. pumping action.
U.S. Pat. No. 8,837,754 B2 recites a method for fabricating a MEMS transducer, which has a micromechanical sensing structure for sensing and a package. The package is provided with a substrate, carrying first electrical-connection elements, and with a lid, coupled to the substrate to define an internal cavity, in which the micromechanical sensing structure is housed. The lid is formed by a cap layer having a first surface and a second surface, set opposite to one another, the first surface defining an external face of the package and the second surface facing the substrate inside the package; and a wall structure, set between the cap layer and the substrate, and having a coupling face coupled to the substrate. At least a first electrical component is coupled to the second surface of the cap layer, inside the package, and the coupling face of the wall structure carries second electrical-connection elements, electrically connected to the first electrical component and to the first electrical-connection elements. However, using microvalves and MEMS transducers for controlling the bulging is not mentioned in these latter two documents. Even further, the MEMS and strain gauges are only used to measure and there is no mention of any other use, let alone control.
The present invention therefore relates to an improved reactor assembly, and use thereof, which solve one or more of the above problems and drawbacks of the prior art, providing reliable results, without jeopardizing functionality and advantages.